Help me design a mid top speaker for my system

Yes, multiple drive units covering the same frequency range will interact with each other, which can cause the response to change as your position relative to the speakers changes. Unless you can achieve the desired output with a single drive unit there is not much you can do.

Your main problem is not so much the 10” drive units, but the compression driver and horn. The horn/waveguide, is fairly small, and the drive unit has a recommended crossover of 1.6KHz. For better results, the crossover should be no more than about 1KHz or even lower (which your drive unit can't manage).

I would stick with just a simple enclosure similar to the X10 shown on this site. Obviously, you will need to retune the cabinet for your particular 10” drive units, but they will at least give some useful output up to the crossover frequency.

Unless the journey is the destination; i.e. the design and building is what you are into, I would not recommend using angled baffles or horn loading. The raw response is not good, and requires processing to get a flat response. Also, the output drops off significantly above 1KHz so you would need to be crossing over to the compression driver at no higher than 800Hz – 900Hz, preferably lower.

The X10 design specifies the Paudio 740N. I think the N stands for neodymium. The same driver is available with a ceramic magnet (BM 740), which is about as cheap as it goes. Presumably a reasonable number of people must have used them to be able to give an opinion. I’ve got some of the original BM 750 drive units, which are basically the same but with a 2” throat as opposed to 1.4”; I cross them over at 900Hz @ 24dB/oct. For the price they work well (My comparison is with B&C, RCF and Faital Pro drive units). I use custom built horns, but a quick check on the internet would suggest there is a greater choice of horns for 1.4” drive units than 2” so probably the way to go.

My experience with commercially available horns is limited, but go with one that is close to the width of your front baffle, which will be around 30cm with 10” drive units. Stay away from the narrow letterbox style mouths and get as close to a square as you can. If you are restricted on the overall height of the cabinet that might restrict things a bit, as could be availability where you live.

Before going out and spending more money, try the compression drivers/horns that you have. If you have an upgrade path in mind just design the front baffle (and cabinet depth) to accommodate  the new horns if you do change them.

The Faital Pro are undoubtedly fine drive units, and are my current personal choice, but the HF146 is twice the price of the Paudio driver. I suppose it depends on what you consider not very expensive. In my opinion the Paudio are better value for money.

If DiegoALM has limited funds, I would still recommend building a system using the components at hand. The decision to upgrade, if necessary, can be made later.